Technical Field
The present invention relates to a battery monitoring apparatus, in particular, a battery monitoring apparatus that monitors a state of a nickel hydrogen battery.
Related Art
As a secondary battery for a vehicle in which the driving force is generated by an electric motor, a nickel hydrogen battery is known. The nickel hydrogen battery has a negative electrode made of a hydrogen storing alloy and a positive electrode made of a nickel compound such as nickel hydroxide. The nickel hydrogen battery is usually incorporated in a vehicle as an assembled battery in which a plurality of cells are connected in series to increase the output voltage. In the vehicle incorporating such a nickel hydrogen battery is generally equipped with a battery monitoring apparatus for monitoring a state of the battery (e.g. refer to JP-A-2002-315212). In the nickel hydrogen battery, the cells are generally grouped into blocks. The battery monitoring apparatus detects a voltage of each of the blocks to monitor the voltage of the assembled battery.
A battery monitoring apparatus for a nickel hydrogen battery is known in which a circuit board, on which electronic components are mounted, is accommodated in a housing. The circuit board is provided with a high-voltage part having a voltage detection circuit for detecting a voltage of an assembled battery, and a low-voltage part having a low-voltage circuit that operates at voltage lower than that of the high-voltage part. The low-voltage part has a function, for example, of outputting a signal corresponding to the detection voltage of the voltage detection circuit to an upper ECU (e.g. hybrid ECU).
When an abnormity is caused in the assembled battery or the voltage detection circuit, the low-voltage part outputs information on the abnormity of the high-voltage part to the upper ECU. Thereby, the abnormity can be detected by the upper ECU. In this case, when an abnormity such as a fault of the voltage detection circuit due to a short circuit is caused, the temperature of the high-voltage part may be higher than usual. If such an abnormity is caused, it is required that the low-voltage part is protected from the high-voltage part whose temperature has become higher. Specifically, the state of the nickel hydrogen battery is often monitored in block voltage. Hence, in the battery monitoring apparatus, the temperature of the high-voltage part easily becomes higher.